Modern technology has enabled microelectromechanical systems (MEMS) to be fabricated on semiconductor substrates, typically silicon substrates. These MEMS typically have sizes in the order of microns and may be integrated with other electrical circuits on a common substrate. As a result, MEMS have found their way into numerous applications across numerous industries. Exemplary MEMS applications include optical switching, inertial or pressure sensors, and biomedical devices.
MEMS optical switches are used in a variety of applications such as switching light waves between optical waveguides, such as fiber optical waveguides. MEMS optical switches are operable in a plane of a substrate or normal to the substrate. An example of an in-plane optical switch using a vertical mirror is disclosed in C. Marxer et al., “Vertical Mirrors Fabricated By Reactive Ion Etching For Fiber Optical Switching Applications,” Proceedings IEEE, The Tenth Annual International Workshop on Micro Electro Mechanical Systems, An Investigation of Micro Structures, Sensors, Actuators, Machines and Robots (Cat. No. 97CH46021), IEEE 1997, pp. 49-54. The Marxer optical switch includes a metal coated silicon mirror coupled to a dual comb drive actuator. The dual comb actuators work in opposite directions to push the mirror into an optical path between optical fibers and to pull the mirror out of the optical path. The Marxer optical switch is fabricated in a single step using inductively coupled plasma etching technology with a sidewall passivation technique.
Various changes have been made in the design of in-plane optical switches using a vertical mirror. One of the changes is the use of a single comb drive actuator, an example of which is disclosed in U.S. patent application, Ser. No. 09/372,265, filed Aug. 11, 1999, entitled “MICROELECTROMECHANICAL OPTICAL SWITCH AND METHOD OF MANUFACTURE THEREOF”, commonly assigned to ADC Telecommunications, Inc., which is incorporated herewith by reference.
With the existing MEMS optical switch technology, the switch that can be formed on a single substrate is a 1×2 optical switch as shown in FIG. 1A. In a 1×2 switch, an input beam is split into two output beams. If an 1×4 optical switch is to be constructed using the existing technology, three 1×2 optical switches are typically cascaded together as shown in FIG. 1B. The cascaded optical switches are coupled to one another by fibers. In general, insertion or coupling losses are associated with fiber couplings. Further, alignment between the fibers can be problematic, which often causes additional insertion or coupling losses. Furthermore, each 1×2 optical switch is typically packaged in a separate package as it is difficult to package several 1×2 optical switches into a single package. As a result, a typical 1×4 optical switch is less compact and involves complicated connections/couplings among the cascaded 1×2 optical switches.
Therefore, improvements on switching efficiency and compactness in fabrication and packaging of optical switches are desired.